1. Field of the Invention
The present invention relates to a method of designing a patterned magnetic recording medium having a patterned magnetic film and also relates to a patterned magnetic recording medium. The patterned magnetic recording medium of the present invention is applied to a magnetic recording apparatus mounted on various recording apparatuses such as computers and video recorders.
2. Description of the Related Art
A perpendicular magnetic recording system attracts attention as a technology for improving the recording density of a magnetic recording medium. In this system, a magnetic thin film of a fine particle structure having perpendicular magnetic anisotropy is used as the recording medium, and information is recorded in the recording medium by a magnetic head in a form of fine magnetization patterns. In the perpendicular magnetic recording system, adjacent magnetizations with a magnetization transition interposed therebetween are coupled antiparallel with each other. Therefore, compared with the longitudinal magnetic recording system, the perpendicular magnetic recording system can maintain a more stable recorded state against thermal magnetic relaxation, making it possible to achieve a higher recording density.
However, it is necessary to reduce the size of the fine particles of the recording medium about one tenth in accordance with decrease in a recording bit length in the perpendicular magnetic recording system, as in the longitudinal magnetic recording medium. In this connection, the magnetic energy of the magnetic particles is decreased so as to bring about influence of the thermal magnetic relaxation. In order to increase the magnetic energy of the magnetic particles, it is effective to increase the magnetic anisotropy of the magnetic material. However, this also increases magnetic field strength required for magnetic reversal in recording, which gives rise to a problem that it is impossible to perform recording using an actual magnetic head.
As a method for breaking through the limit due to the thermal magnetic relaxation phenomenon in the magnetic recording medium, patterned magnetic recording media in which the area of a magnetic dot corresponds to the size of a bit are proposed (Charles T. Rettner, Margaret E. Best and Bruce D. Terris, “Patterning of granular magnetic media with a focused ion beam to produce single-domain islands at >140 Gbit/in2,” IEEE Transactions on Magnetics, volume 37, issue 4, pp. 1649-1651, July 2001”; and Tsutomu Aoyama, Isamu Sato and Shunji Ishio, “Fabrication and magnetic properties of patterned magnetic recording media”, OYO BUTURI, Vol. 72, No. 3, p. 0298-0303 (2003)). Since the area of a magnetic dot corresponds to the size of a bit, the patterned magnetic recording medium can take significantly high magnetic energy, with the result that the medium can ensure the thermal magnetic stability without increasing the magnetic anisotropy. However, there has not been known to date a method of designing a patterned magnetic recording medium taking comprehensive conditions including the thermal magnetic stability, recording facility, ease of fabrication and shift margin of a write head in the cross track direction in recording into consideration. Also, there has not been known an optimum structure of the patterned magnetic recording medium. In the patterned magnetic recording medium, the track width is reduced and, thus, high tracking accuracy is required. Nevertheless, even in patterned magnetic recording media aimed at an areal recording density of 1 Tbit/in2, it is only studied how to satisfy the thermal magnetic stability and the recording conditions or it is only studied the size of the magnetic dot which satisfies the desired density.